The present invention relates to an optical device such as a display device for a numerical or character display, or an X-Y matrix display, and an optical filter capable of controlling transmissivity or reflectance of light, and to an electrolytic solution used for such an optical device.
In voltage-driven display devices such as digital clocks for displaying time, there have been adopted electrochromic materials (hereinafter referred to as EC materials).
A display device using the electrochromic material, an electrochromic display element (hereinafter referred to as ECD), is a non-light-emitting display device which performs a display with a reflected or transmitted light as an electrochemical light adjusting element. Thus, they have advantages not to make observers fatigue even for a long time observation, to be driven at a relatively low voltage, and to consume less power. For example, as disclosed in Unexamined Published Japanese Patent Application No. 59-24879, a liquid type ECD is well known in which a viologen molecular derivative of organic molecular family reversibly forming colored or colorless state is used as an EC material.
However, when an EC material such as a viologen molecular derivative or the like was used in an ECD element, its response and light shielding were so insufficient as those required in an actual device that it has never been put in practical use so far. Furthermore, in spite of the requirement that the device must be able to control the light transmissivity in the visible light region (400 to 700 nm in wavelength) as a light quantity adjusting device, none of EC materials having been used so far have not well satisfied such requirement.
Under such circumstances, the inventors have noticed to apply deposition or dissolution of metallic salt to a light adjusting element as a substitute for ECD, and have carried out development of an electrochemical light adjusting element to which deposition or dissolution of silver is applied. As a result, the inventors have obtained an element with aimed characteristics in both the response and the light shielding.
In spite of this, there was still found a problem that an element using a solvent such as dimethylsulfoxide (DMSO) with high solidifying point (18.degree. C. in DMSO) was, despite the high reversibility of silver deposition and dissolution, so poor in low temperature characteristics as to be easily solidified at low temperature.
An object of this invention is therefore to provide an optical device that can be driven with a low power consumption, can control the transmissivity or reflectance of light in the visible region, and furthermore, has satisfactory low temperature characteristics, as well as an electrolytic solution used for the optical device.